Abstract

Precise surface functional groups, low sp2 content, and controlled size of agglomerates are the major concerns for using nanodiamonds (NDs) successfully in many biological applications. In this context, we report on the surface modifications of NDs carried out in the temperature range from 450 °C to 750 °C via rapid thermal annealing (RTA). Advantage of RTA is that one can obtain sufficient quantity of final sample. Effects on the ND's surfaces have been scrutinized using Fourier transform infrared spectroscopy(FTIR),Raman spectroscopy,photoluminescence, and time-resolved photoluminescencespectroscopy.FTIR shows red-shift in C=O stretching frequency at 450 °C while at 550 °C and above the surface functional groups are either reduced or completely removed. Raman spectrum shows red-shift and peak broadening of diamond peak with increasing temperature from R.T. to 550 °C. The band characteristic to the graphite at 1585 cm−1 is not observed for oxidative temperatures at 550 °C and 650 °C. Raman measurements indicate that the size and surface of NDs are modified. Intriguingly, sharp increase in the PL intensity has been observed at 450 °C, while PL intensity decreases gradually at 550 °C and 650 °C. Comparison of the lifetime decay profile approximated with two exponential components, for the NDs, before and after oxidative treatments at 450 °C indicates that the photoluminescence decay is highly sensitive to the surface modifications due to oxidation. Substantial changes in the luminescence and its decay provide useful insights into the role of the graphite and disordered carbon shell.

Received 03 January 2013Accepted 04 March 2013Published online 20 March 2013

Acknowledgments:

The authors would like to thank National Science Council of Taiwan, R.O.C for financial support through Grant No. NSC-100-2120-M-259-002. Thanks to Professor M. S. Wong (Department of Materials Science and Engineering, National Dong Hwa University, Taiwan) for providing Rapid Thermal Annealing furnace for this work.